The Islamic State group is protecting its largest territory by building a moat around the northern Iraqi city of Mosul. The construction plan comes as President Barack Obama and foreign leaders have vowed to take back the largest city in the militant group's so-called caliphate.

ISIS also plans to build tunnels across the city to block government troops, set out explosives and shut down certain neighborhoods to further bolster its security. Oil tanks are being positioned along the city's border to create a circle of fire should troops reach Mosul,  Reuters reported Wednesday.

"I can see Daesh digging tunnels everywhere and covering the entrances with sewage covers. My neighbour's house is now part of a network of tunnels that reaches across the city," a resident from the Sumer district of southeastern Mosul told Reuters.

Mosul, home to 2 million people and Iraq's second largest city, fell to ISIS in 2014. It quickly became the epicenter of the militant network, with its leader Abu Bakr al-Baghdadi declaring a modern caliphate spanning large parts of Iraq and Syria from the city's main mosque. Iraqi-based Alsumaria TV recently claimed that al-Baghdadi had been spotted in Mosul amid the military struggle.

Iraqi and U.S. officials are expected to launch a battle to reclaim the territory in October. Military leaders in Syra and Iraq have already seized back control of various former ISIS territories, weakening the militant group's vision for a caliphate that would stretch across the Middle East. 

"Oil trenches, tunnels and suicide attacks will not save Daesh from defeat but they will make the battle more challenging," Sabah al-Numani, a spokesman for the counter-terrorism forces leading the offensive, told Reuters. "We are confident Daesh will fight to their last fighter to keep holding Mosul."

Iraqi Prime Minister Haider al-Abadi has vowed to free Mosul by the end of the year. The war is expected to take a significant toll on civilians with a flurry of fires, airstrikes and homemade bombs.

President Barack Obama meet with Abadi in New York Monday ahead of the United Nations General Assembly to assure the Iraqi leader that U.S. officials supported the campaign. 

"This is going to be a challenging battle. Mosul is a large city and ISIL has embedded itself deeply within that city," Obama later told reporters, referring to the militant group by an acronym. "Hopefully by the end of this year we will have seen further progress with respect to Mosul and ... further progress with respect to economic and political stabilization inside of Iraq."

As part of the campaign for Mosul, Iraqi forces announced Tuesday a plan to take back the nearby city of Shirqat from ISIS control.

Source: Graphiq